The widespread deployment of large, interconnected computer system networks has transformed the nature of communication. The largest such network, the Internet, is a general purpose, public computer network which allows millions of computers all over the world, connected to the Internet, to communicate and exchange digital data with other computers also coupled to the Internet.
ATM (Asynchronous Transfer Mode) is a network technology for both local and wide area networks (LANs and WANs) and the Internet that supports realtime voice and video as well as data. ATM technology is often deployed on such networks because of its ability to provide consistent network connections. The ATM topology uses switches that establish a logical circuit from end to end, which guarantees quality of service (QoS). However, unlike telephone switches that dedicate circuits end to end, unused bandwidth in ATM's logical circuits can be appropriated when needed. For example, idle bandwidth in a videoconference circuit can be used to transfer data. ATM is widely used as a backbone technology in carrier networks and large enterprises.
Consistent QoS is highly dependent on the efficiency of routing protocols implemented by the networks. PNNI (Private Network-to-Network Interface) is a routing protocol used between ATM switches in an ATM network. PNNI lets the switches inform each other about network topology so they can make appropriate forwarding decisions. A primary objective of PNNI is to enable ATM switches to dynamically reroute packets based on current network line conditions.
The PNNI specification was developed by the ATM Forum to provide a crankback mechanism to do alternate routing when the connection setup in progress encounters a failure in the network. In such a case, when a connection problem or failure is detected, the specification defines the manner in which the switches reroute a connection to avoid the problem.
However, there is a limitation in the ATM Forum PNNI specification with respect to crankbacks. The problem is how the crankbacks are handled by the entry border nodes in the multi-peer group networks. In multi-peer group networks, the nodes in a peer group know only about the nodes within the peer group and have only summarized information of nodes outside the peer group. Due to this information being aggregated, the exact crankback location cannot be specified outside the peer group.
If the entry border of a peer group cannot route a call to the destination and if the cause of call failure is within the peer group, then, according to the ATMF PNNI specification, the entry border node specifies that the crankback has occurred at the next higher level. This is because the entry border node cannot exactly specify to the source node which peer groupe node has the failure.
This higher level crankback is translated to a blocked node of the logical group node and so, the source node processing this crankback would treat the whole peer group as blocked. If this entry border node crankback happens on the destination peer group, or if it happens on a transit peer group that is the only route to reach the destination node, then the calls and/or connections will never get routed. The failure to complete the call, even though sufficient ATM switch resources are available to do so, defeats the purpose of QoS configuration of the ATM switches. This problem has been widely observed in many multi-peer group deployments. There is no solution available through PNNI or other standards.
Thus, what is needed is a solution that can efficiently handle crankback rerouting in multi-peer group networks. The needed solution should be compatible with existing network standards.